Egypt's public prosecutor charged former President Mohamed Morsi and 35 other top Islamists today with conspiring with foreign groups to commit terrorist acts in Egypt, in a case that could result in their execution.

Declaring it "the biggest case of conspiracy in the history of Egypt", a statement detailed a "terrorist plan" dating back to 2005 and implicating the Palestinian group Hamas, the Shi'ite Islamist government of Iran and its Lebanese ally Hezbollah.

Hamas, which governs the Gaza Strip, dismissed it as "fabrications and lies". There was no immediate comment from Iran, Hezbollah or Morsi's Muslim Brotherhood, most of whose leaders are in prison.

It marks a further escalation in the suppression of an Islamist movement that propelled Morsi to victory in last year's presidential election but which has been driven underground since the army deposed him in July after mass protests.

The state has cracked down hard on the group since then, killing hundreds of its supporters. Thousands more have been arrested as the army-backed government proceeds with a transition plan designed to lead to elections next year.

The next step is a referendum on a new constitution set for mid-January. In a statement today, the Brotherhood's Freedom and Justice Party called for a boycott of the vote.

The previous constitution was written by an Islamist-dominated assembly and signed into law by Morsi a year ago after it was approved in a referendum.

The new constitution contains an article that would ban all religious parties. Although the Brotherhood and its Islamist allies oppose it, the ultraorthodox Islamist Nour Party is calling on Egyptians to vote for the constitution.

DIVULGING MILITARY SECRETS

Besides Morsi, the prosecutor charged Brotherhood leaders Mohamed Badie, Khairat El-Shater, Mahmoud Ezzat and others with crimes including committing acts of terrorism in Egypt and divulging military secrets to a foreign state.

"The idea that the president of the republic is guilty of espionage is a very strange one," said Nathan Brown, a George Washington University professor and expert on Egypt.

"As long as the treatment of the Brotherhood leadership is treated as a security matter rather than a political matter Egypt's political future will remain shaky," he said.

The Brotherhood has said it is committed to peaceful resistance. Its supporters are holding almost daily protests on university campuses against what they see as a bloody military coup against Egypt's first democratically-elected leader.

The prosecutor's statement said the Brotherhood had hatched a plan dating back to 2005 that would send "elements" to the Gaza Strip for military training by Hezbollah and the Iranian Revolutionary Guards.

Upon their return to Egypt, they would join forces with extremist groups in the Sinai Peninsula, the Egyptian-controlled territory that borders Israel to the east, it said.

After the 2011 uprising that ousted President Hosni Mubarak, the group exploited the chaos to carry out attacks on security forces in North Sinai and elsewhere, it said.

The statement said they aimed to establish an "Islamic emirate" in North Sinai were Morsi not declared president.

It added that Morsi's presidential aides including Essam El-Haddad, his national security adviser, had leaked secret reports to Iran's Revolutionary Guards and Hezbollah as a reward for their cooperation.

The charges also accused the Brotherhood of carrying out attacks on security forces in North Sinai after his removal, a reference to an insurgency by hardline Islamists that has escalated since July, killing 200 policemen and soldiers.

Hamas, an ideological cousin of the Muslim Brotherhood, has been demonized by Morsi's opponents in Egypt. Sami Abu Zuhri, the group's spokesman, said the accusations were "empty and meaningless".

The prosecutor was accusing Hamas of "intervening in the internal affairs of Egypt in order to settle purely internal conflicts in Egypt", he said.

Appearing on trial earlier this month, Brotherhood General Guide Badie denied the group had committed any acts of violence.

Morsi is already standing trial for inciting violence during protests outside the presidential palace a year ago when he was still in office.